1. Field of the Invention
The present invention generally relates to sputter deposition and, more particularly, to a method and apparatus for performing a multi-step sputter-deposition process comprising a deposition interval and a forming interval.
2. Description of the Related Art
Sputtering-type physical vapor deposition, (sputter deposition or sputtering), is a thin film deposition method that, compared to many other deposition methods, utilizes relatively simple components, is comparatively inexpensive, and has high process throughput. As a result, sputtering is a desirable method for depositing thin films for applications such as integrated circuit manufacture.
As the feature sizes in integrated circuits become smaller, the demands placed on sputter deposition increases significantly, particularly with respect to film uniformity and step coverage. For example, the current generation of integrated circuits requires high-aspect ratio features with dimensions less than about one quarter of a micron.
Conventional sputtering processes sputter deposit material across a wide angular distribution that typically has a cosine dependence about the target. Such a wide distribution is disadvantageous for filling a high aspect ratio structure. This is because the material that is sputtered from the target in a direction that is not nearly perpendicular to the substrate (i.e., the off-angle portion of the sputtering distribution), preferentially deposits around the upper corners of the high aspect ratio structure forming overhangs. Large overhangs on the high aspect ratio structures restrict the deposition of barrier material therein and at a minimum cause inadequate coverage or substantial thickness variations along the sidewalls and bottom surfaces thereof. While there are a number of techniques used in the art to improve step coverage in PVD processes that are used to deposit material in high aspect ratio features, each technique has its drawbacks.
Therefore, a need exists for a method and apparatus for sputter depositing material into high aspect ratio features such that the sputtered film has a high degree of step coverage and uniformity.
Embodiments of the present invention generally provide a method and apparatus for sputter depositing a film on a substrate. The method comprises, in a deposition interval, applying DC power to a target within a chamber and using a sputtering working gas to sputter material from the target onto the substrate. In a forming interval, that follows the deposition interval, the DC power applied to the target is disconnected and a high frequency power is applied to the target.
During the deposition interval, a sputtering working gas admitted to the chamber has a first pressure. The DC power is applied to the chamber, igniting the working gas to form a plasma. The sputtering working gas sputters material from the target onto the substrate and forms an intermediate layer thereon. During the forming interval, the pressure of the sputtering working gas is increased to a second pressure. A high frequency power is applied to the target to form a plasma that will sputter material from the bottom of a feature on the substrate. As this material is sputtered from the bottom of the feature, the material may be redeposited on a sidewall of the feature. To enhance the ability of the plasma to remove material from the feature on the substrate, a bias power may be applied to a wafer support pedestal during the forming interval.